Method and apparatus for driving edge-emission type electroluminescent elements, method and apparatus for driving a line head having a plurality of edge-emission type electroluminescent elements and image forming apparatus for forming image data on

Abstract

An apparatus for driving edge-emission type electroluminescent elements to emit light to expose an image carrier and to form image data clearly on the image carrier. The edge-emission type electroluminescent elements have electrodes and emit light when a potential difference across the electrodes exceeds a preset threshold value. Electric pulses are supplied to the electrodes of the edge-emission type electroluminescent elements to cause the potential difference across the electrodes to exceed the preset threshold value so that the edge-emission type electroluminescent elements emit light. A series of pulses are supplied for each pixel of image data. The series of pulses includes a first set of pulses supplied at a first cycle to cause the edge-emission type electroluminescent elements to emit light to expose the image carrier, and a second set of pulses supplied at a second cycle slower than the first cycle to cause the edge-emission type electroluminescent elements to emit light to maintain exposure of the image carrier.

What is claimed is: 
     
       1. A method for driving edge-emission type electroluminescent elements to emit light to expose an image carrier and to form image data clearly on the image carrier, comprising: a one-pixel starting step of supplying a first set of pulses of a series of pulses forming one pixel of image data to electrodes of the electroluminescent elements at a first cycle, the first set of pulses causing a potential difference across the electrodes to exceed a preset threshold value at which the electroluminescent elements emit light; and   a one-pixel ending step, continuous with said one-pixel starting step, of supplying a second set of pulses of the series of pulses forming one pixel of image data to the electrodes of the electroluminescent elements at a second cycle slower than the first cycle, the second set of pulses causing a potential difference across the electrodes to exceed the preset threshold value at which the electroluminescent elements emit light; and   wherein the electroluminescent elements emit sufficient light during said first set of pulses to cause the image carrier to be exposed, and emit sufficient light during said second set of pulses to maintain exposure of the image carrier.   
     
     
       2. The method according to claim 1, wherein said pulses alternately generate positive-phase and inverted-phase potential differences across the electrodes exceeding the preset threshold value at which the electroluminescent elements emit light. 
     
     
       3. A method for driving a line head having a plurality of edge-emission type electroluminescent elements having common electrodes and channel electrodes to form a latent image on an image carrier by exposing the image carrier with a prescribed quantity of light, including the steps of: supplying a first set of pulses of a series of pulses to the common electrodes of the electroluminescent elements at a fast cycle to rapidly increase emission of light from the electroluminescent elements to the prescribed quantity to expose the image carrier;   subsequently supplying a second set of pulses of the series of pulses to the common electrodes of the electroluminescent elements at a slow cycle slower than the fast cycle to maintain emission of light from the electroluminescent elements above the prescribed quantity to maintain exposure of the image carrier; and   wherein pulses are supplied to the channel electrodes of the electroluminescent elements in synchronism with the supply of the first series of pulses to the common electrodes to selectively cause a potential difference across the common electrodes and channel electrodes to exceed a predetermined value at which the electroluminescent elements emit light.   
     
     
       4. The method according to claim 3 further including a step of counting a number of pulses supplied to one of the common electrodes of the electroluminescent elements, and a step of changing the supply of pulses to the common electrode from the first set of pulses to the second set of pulses when the counted number of pulses reaches a prescribed value. 
     
     
       5. An apparatus for driving edge-emission type electroluminescent elements to emit light to expose an image carrier and to form image data clearly on the image carrier, comprising: edge-emission type electroluminescent elements having electrodes and emitting light when a potential difference across the electrodes exceeds a preset threshold value;   power supply means for supplying electric pulses to the electrodes of the edge-emission type electroluminescent elements to cause the potential difference across the electrodes to exceed the preset threshold value so that the edge-emission type electroluminescent elements emit light; and   pulse control means for controlling the power supply means to supply a series of pulses for each pixel of image data, said series of pulses comprising a first set of pulses supplied at a first cycle to cause the edge-emission type electroluminescent elements to emit light to expose the image carrier, and a second set of pulses supplied at a second cycle slower than the first cycle to cause the edge-emission type electroluminescent elements to emit light to maintain exposure of the image carrier.   
     
     
       6. The apparatus according to claim 5, wherein said pulse control means controls the power supply means to alternately generate positive-phase and inverted-phase potential differences across the electrodes exceeding the preset threshold value at which the electroluminescent elements emit light. 
     
     
       7. An apparatus for driving a line head having a plurality of edge-emission type electroluminescent elements to form a latent image on an image carrier by exposing the image carrier with a prescribed quantity of light, comprising: supply means for supplying a series of pulses to the edge-emission type electroluminescent elements to selectively cause the edge-emission type electroluminescent elements to generate light;   control means for controlling the supply means to supply a first set of the series of pulses at a first cycle to cause the edge-emission type electroluminescent elements to rapidly emit light to expose the image carrier, and to supply a second set of the series of pulses at a second cycle slower than the first cycle.   
     
     
       8. The apparatus according to claim 7, wherein said control means includes counting means for counting a number of pulses supplied to one of the edge-emission type electroluminescent elements, and changing means for controlling the supply means to change the supply of pulses from the first set of pulses to the second set of pulses when the number of pulses counted by the counting means reaches a prescribed value. 
     
     
       9. An image forming apparatus for forming image data clearly on an image carrier by driving edge-emission type electroluminescent elements to emit light to expose the image carrier, comprising: a line head having an array of edge-emission type electroluminescent elements arranged in a major scanning direction of the image carrier, each edge-emission type electroluminescent element having electrodes and emitting light when a potential difference across the electrodes exceeds a preset threshold value;   power supply means for supplying electric pulses to the electrodes of selected edge-emission type electroluminescent elements on the line head to cause the potential difference across the electrodes of the selected edge-emission type electroluminescent elements to exceed the preset threshold value so that the selected edge-emission type electroluminescent elements emit light, said selected edge-emission type electroluminescent elements being selected on the basis of the image data; and   pulse control means for controlling the power supply means to supply a series of pulses for each pixel of image data, said series of pulses for each pixel comprising a first set of pulses supplied at a first cycle to cause the selected edge-emission type electroluminescent elements to emit light to expose the image carrier, and a second set of pulses supplied at a second cycle slower than the first cycle to cause the selected edge-emission type electroluminescent elements to emit light to maintain exposure of the image carrier.   
     
     
       10. The apparatus according to claim 9, wherein said pulse control means controls the power supply means to alternately generate positive-phase and inverted-phase potential differences across the electrodes of the selected edge-emission type electroluminescent elements exceeding the preset threshold value at which the edge-emission type electroluminescent elements emit light. 
     
     
       11. The apparatus according to claim 9, wherein said line head includes a plurality of blocks, each block having a predetermined number of edge-emission type electroluminescent elements, and wherein said pulse control means time-division controls the supply of pulses to the edge-emission type electroluminescent elements of each block. 
     
     
       12. The apparatus according to claim 11, wherein said power supply means comprises a channel driver connected to each block for applying a voltage to a channel electrode of the edge-emission type electroluminescent elements of each block, and a corresponding common driver connected to each block for applying a voltage to a common electrode of the edge-emission type electroluminescent elements of each block, and wherein said pulse control means time-division controls the supply of voltage to the common electrode of each block.